The present invention relates to a rotary electric machine such as a gas cooled generator. More particularly, the present invention relates to a rotary electric machine having an enhanced cooling effect.
FIG. 19 schematically illustrates a cooling system of a closed type rotary electric machine.
Referring to FIG. 19, reference numeral “1” denotes a closed type rotary electric machine which may typically be a turbine generator arranged in a closed type frame 2. The machine 1 comprises a stator 3 which includes an annular stator core 3-1 and a stator coil 3-2 contained in the slot of the stator core 3-1. The machine 1 further comprises a rotor 4 provided with a field coil (not shown) wound around it and arranged concentrically relative to the stator core 3-2 with an air gap interposed between them. The machine 1 comprises rotor fans 5 fitted to the end sections of the shaft of the rotor 4, and a gas cooler 6 arranged behind (above in the drawing) the stator 3.
Cooling gas 7 such as air or hydrogen gas is contained in the closed frame 2 and is driven by the rotor fans 5 to flow and circulate as indicated by arrows 8 and 9 so as to cool the stator 3 and the rotor 4. The cooling gas 7 that has been warmed is then cooled by a gas cooler 6.
While the flow path of cooling gas 7 in the rotary electric machine 1 is schematically illustrated in FIG. 19 in a simplified manner, the actual gas flow path is a complex one as the stator core 3-1 is divided by a gas guide plate into a gas supply section and an exhaust section as shown in FIGS. 12 and 13 of Japanese Patent Application Laid-Open Publication No. 2001-29806 (the entire contents of which are incorporated herein by reference).
The above-described gas cooler 6 is provided with a heat exchange tube 13 typically formed by using a finned tube. As cooling water that is at about 30 to 40° C. is supplied into the heat exchange tube 13 from a main cooling water system 10, the cooling gas 7 is cooled to about 40 to 50° C. In FIG. 19, reference numeral “11” denotes the supply port of the cooling water system and reference numeral “12” denotes the discharge port of the cooling water system. While only a single gas cooler 6 is shown in the schematic view of FIG. 19, normally a plurality of gas coolers are arranged in series, in parallel or in series-parallel. While tap water is normally used as coolant, antifreeze liquid, river water, sea water or some other liquid coolant may alternatively be used under certain circumstances. Therefore, cooling water is referred to as main cooling water here.
While the cooling gas 7 contained in the closed frame 2 is driven to flow and circulate to cool the stator 3 and the rotor 4 in the above-described cooling system, such a cooling system may not be sufficient when the rotary electric machine 1 is a large capacity machine. Then, a water-cooled stator coil system is adopted in addition to the above-described cooling system. With a water-cooled stator coil system, the stator coil 3-2 of the rotary electric machine comprises hollow conductors and a coolant is made to flow in the hollow part of the stator coil 3-2 to directly cool the stator coil 3-2 (See Japanese Patent Application Laid-Open Publication No. (Hei)11-98767). FIG. 20 schematically illustrates the arrangement for cooling a stator coil by means of a water-cooled stator coil system. This arrangement will be described below.
In the case of a rotary electric machine additionally provided with a water-cooled stator coil system, the cooling gas 7 is driven to flow and circulate in the machine so as to cool the components of the machine other than the stator coil 3-2. Thus, the arrangement of the circulation path and the heat transfer route of the cooling gas 7 and the configuration of the main cooling water system 10 are similar to those schematically illustrated in FIG. 19. Therefore, the gas cooler 6 and the arrows 8, 9 indicating the flow of the cooling gas 7 are not shown in FIG. 20.
Pure water is used as coolant to be flown into a stator coil 38 that is electrically energized in a rotary electric machine with a water-cooled stator coil system because pure water is electrically highly insulating. While pure water is supplied from a pure water supply system 36 comprising a pure water producing apparatus, a pure water storage tank and a circulating pump, although not shown in FIG. 20.
Referring to FIG. 20, the pure water is pressurized by a circulating pump (not shown) arranged in the pure water supply system 36 and supplied to the stator coil 38 in the rotary electric machine 1 by way of a collecting tube such as one of the headers. Then, it flows in the stator coil 38 in the axial direction to directly cool the stator coil 38. The pure water that is warmed as a result of cooling the stator coil 38 is collected in a collecting tube such as the other header and taken out to the outside of the rotary electric machine 1. Then, it is cooled in a pure water cooler 37 as a result of heat exchange with cooling water to become ready for flowing again to the pure water supply system 36 to circulate.
The upper limit of the temperature of the stator coil 3-2 and that of the rotor coil of a rotary electric machine of the type under consideration are strictly defined because of the thermal limit of the insulations of the coils.
On the other hand, the temperature of the cooling gas 7 that has exchanged heat in the gas cooler 6 indicated by the arrow 9 in FIG. 19 is influenced by the temperature of the cooling water that is supplied to the gas cooler 6. Since the temperature of the cooling water that is being supplied can vary depending on the machine, the temperature rise that the stator coil 3-2 and other components are allowed also varies from machine to machine. Thus, there is a problem that the dimensions and the flow rate of cooling gas to be used have to be designed for each rotary electric machine.
Additionally, when rotary electric machines of the same design are applied to different cooling water temperatures, there is a problem that the output of the rotary electric machine is limited due to the temperature limitation when the temperature of the cooling water that is actually supplied is higher than the design temperature of cooling water, whereas an unnecessarily large rotary electric machine has to be applied when the temperature of the cooling water that is actually supplied is lower than the design temperature of cooling water.
Still additionally, since rotary electric machines are generally designed to achieve the highest efficiency at the design point, there is a problem that the efficiency of the rotary electric machine decreases when it is driven to operate with a cooling water temperature that is different from the design temperature.
In view of the above-identified circumstances, it is therefore an object of the present invention to provide a rotary electric machine that can be driven to operate when the temperature of the cooling water supplied to the gas cooler thereof varies and is applicable to various conditions of cooling water and a wide capacity range with the same design of the rotary electric machine main body and also capable of being operated efficiently responding to the operating condition of the machine.